Suction cups have been used on many devices in the office as well as in the home for a long time, and the way in which a suction cup works is well known. In essence, a resilient and air-tight concave body is pressed against a surface. The periphery of the body forms an air-tight seal with the surface, and when the center of the body pulls resiliently away from the surface, a partial vacuum is formed between the body and the surface so that the body "sticks" to the surface. The greater the vacuum the better the cup sticks to the surface.
One factor which limits the degree of vacuum which can be achieved is the vacuum itself--the vacuum resists the resilient force of the body so that the force of suction balances the resilient force of the body of the suction cup. However, if one could "pull" the center of the body away from the surface, thereby at least partially overcoming the restraining effect of the vacuum, the vacuum can be made even greater.
Several devices have been proposed to "pull" the center of the suction cup away from the surface in order to increase the suction. The most common arrangement, often found for example on the bases of pencil sharpeners and many kitchen appliances, involves a rod or crankshaft which extends mainly parallel to the surface to which the suction cup is to adhere. The center of the suction cup is attached to an eccentric section of the rod or crankshaft, and when a lever arm is turned, the center of the suction cup is pulled outward. U.S. Pat. No. 2,089,714 (Schuler, Aug. 10, 1937); U.S. Pat. No. 3,675,638 (Kampmirer, July 11, 1972); U.S. Pat. No. 3,765,638 (Harrison, Oct. 16, 1973); and U.S. Pat. No. 4,934,641 (McElhaney, June 19, 1990) all describe such shaft-based arrangements.
One problem with arrangements using crankshafts and eccentric rods is that they have lever arms which extend out from whatever device they are mounted in, so that it is all too easy to hit or snag on the arm accidentally and thereby to release the suction. Another drawback of lever arms is that the support and bearing structure for them is difficult to integrate into the structure of the device which is utilizing the suction cups. This complication increases costs and the likelihood of failure.
A further cause of increased costs associated with such suction cup assemblies according to the prior art is that they usually require suction cups that must be specially designed to accommodate the lever arms, crankshafts, and the like.
The object of this invention is consequently to provide a suction cup arrangement which includes a tensioning device for pulling the center of a suction cup away from the surface on which it is to adhere. The tensioning device is simple, highly effective and compact, and eliminates the risk of inadvertent release. Its support structure may be manufactured of easily molded plastic parts, and is easily integrated with the support structure of the suction cup itself. The suction cup itself may be of a readily available shape and material, and little or no special modification is required.